The invention relates generally to synthetic filament yarn fabric for use in the manufacture of an air bag and more particularly to mechanically compressed fabric structures which can be packed into small volumes without unduly affecting air permeability.
Fabrics used for manufacturing air bags are required in general to possess a limited and controlled air permeability. As will be appreciated, such fabrics are generally woven structures formed from synthetic yarns made up of a plurality of individual filaments. Formation of such fabrics may be carried out on weaving machines using air-jet, water-jet or mechanical means for insertion of filling yarns between a plurality of warp yarns in a manner well known to those of skill in the art. Such woven textile materials are disclosed for example in U.S. Pat. Nos. 5,566,434 to Beasley, U.S. Pat. No. 5,508,073 to Krummheuer et al.; U.S. Pat. No. 5,503,197 to Bower et al.; U.S. Pat. No. 5,356,680 to Krummheuer et al.; U.S. Pat. No. 5,421,378 to Bower et al.; U.S. Pat. No. 5,277,230 to Sollars, Jr.; U.S. Pat. No5,259,645 to Hirabayashi et al; U.S. Pat. No. 5,110,666 to Menzel, et al.; U.S. Pat. No. 5,093,163 to Krummheuer et al.; 5,073,418 to Thornton et al.; U.S. Pat. No. 5,011,183 to Thornton et al.; U.S. Pat. No. 4,977,016 to Thornton et al.; U.S. Pat. No. 4,921,735 to Bloch and U.S. Pat. No. 3,814,141 to Iribe et al. (all specifically incorporated herein by reference).
As will be appreciated, very low controlled air permeabilities may be achieved through the use of coatings applied to the fabric construction. The primary coatings of use have been chloroprene (neoprene), silicone and other elastomeric resins. However, the use of such coatings presents a disadvantage from both an economic as well as a functional standpoint. Specifically, the use of coatings may add substantial cost while at the same time adding bulk to the finished product which translates to a greater folded volume of the final configuration thereby requiring a greater allocation of space within the vehicle deployment system.
In the attempt to avoid the use of coatings while at the same time achieving low and controlled air permeabilities, a number of approaches have been taken. The patents to Thornton et al. and Bloch propose the achievement of low permeability through the use of calendering to close the voids at the interstices between overlapping yarns in the fabric. While such calendering operations may reduce permeability, such operations also generally stiffen the fabric thereby increasing the volume requirements for a packed bag formed of such calendered material. Fabrics have also been produced using extremely tight weave constructions thereby packing the yarns so tightly together as to achieve the desired low air permeability. One such known construction is a 420 denier nylon 6,6 fabric having 57 threads per inch in the warp and 53 threads per inch in the fill and sold under the trade designation MICROPERM(trademark) by Milliken and Company in LaGrange, Ga. A problem associated with this practice is once again the fact that the fabric produced may have relatively poor foldability due to the very high number of threads per inch within the woven construction which increases the stiffness and hence the packed volume requirement.
Packed volume (i.e. foldability) is becoming an increasingly important feature of air bag fabrics. Specifically, good foldability is crucial if the air bag is to be accommodated in the steering wheel of motor vehicles in the least amount of space. In addition, good foldability also makes possible the trouble-free inflation of the air bag for protecting a vehicle occupant in the event of a collision. Further, these issues of packing and trouble-free inflation become even more important as complex folding patterns are utilized to control initial impact in instances where an occupant may be directly facing the deploying cushion.
The difficulty in improving foldability is that processes which are recognized to generally improve the drape of a fabric and thereby its foldability such as for example, physical, pneumatic or hydraulic impingement practices also tend to dramatically increase the air permeability of the fabric. In U.S. Pat. No. 5,508,073 to Krummheuer et al. (incorporated by reference), it has been proposed that improved foldability of air bag fabric can be achieved without sacrificing air permeability so long as yarns having very low filament linear densities are utilized in the construction.
In light of the above, a need exists for a fabric for use in an air bag which can be produced with improved foldability without sacrificing physical properties and without being restricted to the use of low DPF yarns. The present invention provides such a fabric and methods for producing the same and therefore represents a useful advancement over the state of the art
In recognition of the foregoing and other limitations in the prior art constructions, it is a general object of the present invention to provide an air bag fabric of improved foldability which may be constructed from a broad range of yarn types.
It is a further object of the present invention to provide an air bag fabric of improved foldability wherein such improved foldability is achieved by means of inexpensive mechanical treatment processes without substantially increasing air permeability characteristics of the fabric.
It is yet a further object of the present invention to provide an air bag fabric of improved foldability wherein such improved foldability is achieved by means of mechanical treatment processes which additionally reduce variations in physical properties across the width of the fabric as may be introduced during weaving.
Surprisingly, it has been found that the above objects of improved foldability as measured by packed volume under compressive loading and reduction in physical property variation across the width of the fabric can be achieved by mechanically compressing the fabric without adversely affecting air permeability characteristics.
Accordingly, in one aspect of the present invention a woven fabric constructed substantially of synthetic yarn is provided which has undergone processing by mechanical compression. The compressed fabric has a packed volume per unit area of fabric which is less than the packed volume per unit area of the fabric prior to mechanical compression.
In another aspect of the present invention, a woven fabric constructed substantially of synthetic yarn is provided which has undergone processing such that the compressed fabric has a packed volume per unit area of fabric which is less than the packed volume per unit area of the fabric prior to processing. In addition, the dynamic air permeability of the fabric is reduced to a level below that of the fabric prior to processing.
Other objects, features and aspects of the present invention will be apparent through reference to the description of preferred embodiments and accompanying figures as set forth below.